[PATCH 3/3] drm/komeda - Fix handling of pending crtc state commit to avoid lock-up
Liviu Dudau
liviu.dudau at arm.com
Mon Jul 11 10:13:17 UTC 2022
On Fri, Jul 08, 2022 at 07:03:37PM +0100, Carsten Haitzler wrote:
>
>
> On 7/8/22 17:02, Liviu Dudau wrote:
> > On Mon, Jun 06, 2022 at 12:47:14PM +0100, carsten.haitzler at foss.arm.com wrote:
> > > From: Carsten Haitzler <carsten.haitzler at arm.com>
> >
> > Hi Carsten,
> >
> > >
> > > Sometimes there is an extra dcm crtc state in the pipeline whose
> > > penting vblank event has not been handled yet. We would previously
> > > throw this out and the vblank event never triggers leading to hard
> > > lockups higher up the stack where an expected vlank event never comes
> > > back (screen freezes).
> > >
> > > This fixes that by tracking a pending crtc state that needs handling
> > > and handle it producing a vlank event next vblank if it had not
> > > laready been handled before. This fixes the hangs and ensures our
> > > display keeps updating seamlessly and is certainly a much better state
> > > to be in than after some time ending up with a mysteriously frozen
> > > screen and a lot of kernle messages complaining about this too.
> >
> > Sorry it took me so long to review and reply to this patch, but I had this nagging
>
> No worries. :)
>
> > feeling that the patch is not actually correct so I've tried to track the actual
> > issue. It turns out that the problem is easy to reproduce in a different setup with
> > Mali D71 and it comes from the fact that Komeda doesn't properly wait for the
> > hardware to signal acceptance of config valid on setting new commits. I have created
> > a new patch that I would be happy if you can test to try to fix the actual issue.
>
> This works (tested).
Thank you very much for testing this! Can I add your Tested-by?
> One errant "flip without commit":
>
> [ 9.402559] fbcon: Taking over console
> [ 9.525373] [drm:komeda_print_events [komeda]] *ERROR* err detect: gcu:
> MERR, pipes[0]: FLIP, pipes[1]: None
> [ 9.525455] [drm] CRTC[0]: FLIP happened but no pending commit.
> [ 9.542215] Console: switching to colour frame buffer device 240x67
>
Is this with your 2/3 patch applied and coming out from the firmware having already
initialised the hardware? If so, the handover probably doesn't quiescence the
interrupts correctly so an interrupt is pending when the kernel driver is
initialised. That's another area worth looking at for the handover purposes.
> But nothing worrying. It does work, though doesn't compile due to:
>
> drivers/gpu/drm/arm/display/komeda/komeda_kms.c: In function
> ‘komeda_kms_atomic_commit_hw_done’:
> drivers/gpu/drm/arm/display/komeda/komeda_kms.c:77:9: error: ‘for’ loop
> initial declarations are only allowed in C99 or C11 mode
> 77 | for (int i = 0; i < kms->n_crtcs; i++) {
> | ^~~
> drivers/gpu/drm/arm/display/komeda/komeda_kms.c:77:9: note: use option
> ‘-std=c9
> ’, ‘-std=gnu99’, ‘-std=c11’ or ‘-std=gnu11’ to compile your code
>
> but that was a trivial fixup.
Interesting that I'm not seeing that, probably due to using GCC12? Anyway, I'll fix
that and send a proper patch.
>
> Your commit handler does sit and wait. I guess I avoided that and had it
> still deferred and handled next time the vblank interrupt fires. Yours is a
> bit shorter and less complex so it wins. :)
Yes, that's the essence of my issue with your patch. Delaying the handling of the
event until the next vblank means older software that doesn't use the timestamping
from the vblank event will get wrong framerates (playing video might be affected).
Waiting here when we're also calling drm_atomic_helper_wait_for_flip_done() after
drm_atomic_helper_commit_hw_done() feels wrong, but then the later is checking if we
have consumed the event so we have to. Maybe the introduction of the
drm_atomic_helper_fake_vblank() is needed in komeda as well like the generic
commit_tail helper function does? I need to investigate more the next time I get some
spare cycles on komeda.
I will send a new email with the updated patch and your Tested-by if that's OK.
Best regards,
Liviu
>
> > --8<---------------------------------------------------------------------------
> >
> > From 76f9e5fed216a815e9eb56152f85454521079f10 Mon Sep 17 00:00:00 2001
> > From: Liviu Dudau <liviu.dudau at arm.com>
> > Date: Fri, 8 Jul 2022 16:39:21 +0100
> > Subject: [PATCH] drm/komeda: Fix handling of atomic commits in the
> > atomic_commit_tail hook
> >
> > Komeda driver relies on the generic DRM atomic helper functions to handle
> > commits. It only implements an atomic_commit_tail hook for the
> > mode_config_helper_funcs and even that one is pretty close to the generic
> > implementation with the exception of additional dma_fence signalling.
> >
> > What the generic helper framework doesn't do is waiting for the actual
> > hardware to signal that the commit parameters have been written into the
> > appropriate registers. As we signal CRTC events only on the irq handlers,
> > we need to flush the configuration and wait for the hardware to respond.
> >
> > Add the Komeda specific implementation for atomic_commit_hw_done() that
> > flushes and waits for flip done before calling drm_atomic_helper_commit_hw_done().
> >
> > The fix was prompted by a patch from Carsten Haitzler where he was trying to
> > solve the same issue but in a different way that I think can lead to wrong
> > event signaling to userspace.
> >
> > Reported-by: Carsten Haitzler <carsten.haitzler at arm.com>
> > Signed-off-by: Liviu Dudau <liviu.dudau at arm.com>
> > ---
> > .../gpu/drm/arm/display/komeda/komeda_crtc.c | 4 ++--
> > .../gpu/drm/arm/display/komeda/komeda_kms.c | 20 ++++++++++++++++++-
> > .../gpu/drm/arm/display/komeda/komeda_kms.h | 2 ++
> > 3 files changed, 23 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/arm/display/komeda/komeda_crtc.c b/drivers/gpu/drm/arm/display/komeda/komeda_crtc.c
> > index 59172acb973803d..292f533d8cf0de6 100644
> > --- a/drivers/gpu/drm/arm/display/komeda/komeda_crtc.c
> > +++ b/drivers/gpu/drm/arm/display/komeda/komeda_crtc.c
> > @@ -235,7 +235,7 @@ void komeda_crtc_handle_event(struct komeda_crtc *kcrtc,
> > crtc->state->event = NULL;
> > drm_crtc_send_vblank_event(crtc, event);
> > } else {
> > - DRM_WARN("CRTC[%d]: FLIP happen but no pending commit.\n",
> > + DRM_WARN("CRTC[%d]: FLIP happened but no pending commit.\n",
> > drm_crtc_index(&kcrtc->base));
> > }
> > spin_unlock_irqrestore(&crtc->dev->event_lock, flags);
> > @@ -286,7 +286,7 @@ komeda_crtc_atomic_enable(struct drm_crtc *crtc,
> > komeda_crtc_do_flush(crtc, old);
> > }
> > -static void
> > +void
> > komeda_crtc_flush_and_wait_for_flip_done(struct komeda_crtc *kcrtc,
> > struct completion *input_flip_done)
> > {
> > diff --git a/drivers/gpu/drm/arm/display/komeda/komeda_kms.c b/drivers/gpu/drm/arm/display/komeda/komeda_kms.c
> > index 93b7f09b96ca950..1a53bd87e81d8ad 100644
> > --- a/drivers/gpu/drm/arm/display/komeda/komeda_kms.c
> > +++ b/drivers/gpu/drm/arm/display/komeda/komeda_kms.c
> > @@ -69,6 +69,24 @@ static const struct drm_driver komeda_kms_driver = {
> > .minor = 1,
> > };
> > +static void komeda_kms_atomic_commit_hw_done(struct drm_atomic_state *state)
> > +{
> > + struct drm_device *dev = state->dev;
> > + struct komeda_kms_dev *kms = to_kdev(dev);
> > +
> > + for (int i = 0; i < kms->n_crtcs; i++) {
> > + struct komeda_crtc *kcrtc = &kms->crtcs[i];
> > +
> > + if (kcrtc->base.state->active) {
> > + struct completion *flip_done = NULL;
> > + if (kcrtc->base.state->event)
> > + flip_done = kcrtc->base.state->event->base.completion;
> > + komeda_crtc_flush_and_wait_for_flip_done(kcrtc, flip_done);
> > + }
> > + }
> > + drm_atomic_helper_commit_hw_done(state);
> > +}
> > +
> > static void komeda_kms_commit_tail(struct drm_atomic_state *old_state)
> > {
> > struct drm_device *dev = old_state->dev;
> > @@ -81,7 +99,7 @@ static void komeda_kms_commit_tail(struct drm_atomic_state *old_state)
> > drm_atomic_helper_commit_modeset_enables(dev, old_state);
> > - drm_atomic_helper_commit_hw_done(old_state);
> > + komeda_kms_atomic_commit_hw_done(old_state);
> > drm_atomic_helper_wait_for_flip_done(dev, old_state);
> > diff --git a/drivers/gpu/drm/arm/display/komeda/komeda_kms.h b/drivers/gpu/drm/arm/display/komeda/komeda_kms.h
> > index 456f3c435719317..bf6e8fba5061335 100644
> > --- a/drivers/gpu/drm/arm/display/komeda/komeda_kms.h
> > +++ b/drivers/gpu/drm/arm/display/komeda/komeda_kms.h
> > @@ -182,6 +182,8 @@ void komeda_kms_cleanup_private_objs(struct komeda_kms_dev *kms);
> > void komeda_crtc_handle_event(struct komeda_crtc *kcrtc,
> > struct komeda_events *evts);
> > +void komeda_crtc_flush_and_wait_for_flip_done(struct komeda_crtc *kcrtc,
> > + struct completion *input_flip_done);
> > struct komeda_kms_dev *komeda_kms_attach(struct komeda_dev *mdev);
> > void komeda_kms_detach(struct komeda_kms_dev *kms);
--
====================
| I would like to |
| fix the world, |
| but they're not |
| giving me the |
\ source code! /
---------------
¯\_(ツ)_/¯
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